Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 252339 AAA
AFDMKX

Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
639 PM CDT Sat Mar 25 2017

.UPDATE...

Patchy drizzle and scattered showers will continue this evening
into the overnight hours. The focus is in the east at the moment,
but should spread westward by late evening. Temps will remain
fairly steady this evening into tonight.

&&

.AVIATION(00Z TAFS)...

Low clouds are expected to persist through Sunday as low pressure
moves slowly northeastward. Scattered showers with patchy drizzle
will continue tonight and Sunday. Could see some lower
visibilities form tonight as the winds become lighter.

&&

.PREV DISCUSSION... (Issued 315 PM CDT SAT MAR 25 2017)

TONIGHT AND SUNDAY - Forecast Confidence...Medium.

A closed upper low over Missouri will drift across Illinois on
Sunday. The weakening surface low will take a similar path, with the
center reaching southern Lake Michigan Sunday afternoon. Periods of
rain associated with vorticity advection will traverse southern WI
from south to north through Sunday.

The next wave of showers is currently over east central IL which
should affect at least southeast WI (not sure how much of south
central WI) from late afternoon through early evening. It looks like
there could be a lull in the precip for the late evening hours, then
another round of more widespread showers is anticipated in southern
WI late tonight into Sunday morning as the upper low gets closer.

Expect low clouds and areas of fog and drizzle in between the rain
all night and through the day Sunday. There is a chance for dense
fog, especially near the lakeshore later tonight into Sunday morning
as winds become light.

SUNDAY NIGHT THROUGH TUESDAY - Forecast Confidence...Medium to
High.

Expect low pressure to further weaken and occlude over the central
Great Lakes Sunday night.  However northern CWA will be close enough
to lingering mid-level circulation to warrant continuing a chance
for some light rain during the evening.  This system will finally
get nudged far enough east of the area by late Sunday night ending
the light rain threat.  Short term guidance in better agreement on
upstream kicker short wave over the central Plains taking a more
easterly track and only potentially grazing southern WI with some
light rain later Monday into Monday night. NAM does show a period of
low level frontogenetical forcing and Q-vector divergence brushing
the far south, while other guidance farther south.  Will keep some
low pops in for this period, but may be removing them in later
forecast packages.

Upstream high amplitude long wave trofing over western CONUS results
n building ridging from southern Canada into the upper Midwest and
Great Lakes Monday night and Tuesday.  So a quiet and dry period
expected with no significant push of colder air so temps to remain
around  near or slightly above seasonal normal for late March.

EXTENDED PERIOD...

TUESDAY NIGHT THROUGH SATURDAY - Forecast Confidence...Medium
trending to Low.

Higher amplitude high pressure ridge should continue to bring quiet,
cool conditions to southern WI through Wednesday.  Despite having a
persistent northeast wind, low level wind speeds and rh look
marginal and 850H temperatures to remain warmer.  Hence no lake
effect precipitation is expected early in the period, however will
have to watch for sct-bkn clouds for a time Tuesday night.

Upstream cutoff low pressure over SW Conus finally gets nudged ENE
beginning Wed.  ECMWF and NH Canadian remain more bullish on taking
this system northeast into the western GtLakes on Friday, while GFS
shows more protective zonal to nw flow across the western Great
Lakes, which diverts the ejecting low well south of the area.  Last
several ECMWF has been slowing system down however and weakening it
to an open wave.  GFS ensembles show quite a bit of variability
beginning Thursday. WPC blended guidance blends GFS and ECMWF
through the period. Main question is how much zonal to NW flow and
high pressure lingers over the Great Lakes later next week. With
upstream kicker digging into the SW Conus, can not rule out either
solution at this time but prefer the faster NE movement. Hence wl
have chance pops for the later periods and fine tune as event draws
closer. Temps to remain near or slightly above seasonal normal.

AVIATION (21Z TAF update)...

Areas in southeast WI have a better chance of more showers late this
afternoon into the early evening. Otherwise, expect drizzle and
light fog to persist through the night. Another round of steadier
rain showers is anticipated early Sunday morning.

IFR and lower ceilings with visibility in the 1 to 3 mile range
expected through Sunday morning as low pressure tracks across
central Illinois. Areas of dense fog are possible, especially toward
Lake Michigan.

MARINE...

Brisk northeast to east winds will gradually diminish overnight as
the surface low approaches Lake Michigan. Waves will be slower to
subside, so the Small Craft Advisory is in effect until early Sunday
morning.

Ample moisture and relatively mild air over the cooler lake is
allowing for fog to develop in southern Lake Michigan. Web cams are
starting to show lower visibilities over the lake toward Kenosha and
Winthrop Harbor. Areas of dense fog with visibility of 1 mile or
less are expected tonight through Sunday morning. A Marine dense fog
advisory is in effect.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Dense Fog Advisory until 10 AM CDT Sunday for LMZ645-646.

     Small Craft Advisory until 7 AM CDT Sunday for LMZ643>646.

&&

$$

Update...DDV
Tonight/Sunday and Aviation/Marine...Cronce
Sunday Night through Saturday...MBK



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